1. Field of the Invention
The present invention generally relates to a brake device for bicycles and the like. More specifically, the present invention relates to a cantilever type bicycle brake device having a linkage mechanism for controlling the movement of the brake shoes against the rim of a bicycle wheel.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has also become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One particular component of bicycles which has been extensively redesigned over the past years is the bicycle brake device. Bicycle brake devices are constantly being redesigned to be lighter and provide additional braking power.
There are several types of bicycle brake devices which are currently available on the market. Examples of some types of common bicycle brake devices include rim brakes and caliper brakes. With respect to caliper brakes, there are mainly three types of caliper brakes: a side pull type, a center pull type and cantilever type. In a side pull type of caliper brake device, a pair of brake arms are pivotally connected together about a center mounting bolt which attaches to the frame of the bicycle. Each of the brake arms has a lever portion which is coupled to the brake wire such that when the rider operates the brake lever of the brake operating device, the lever portions of the brake arms are pulled together, which in turn move the brake shoes attached to the other ends of the brake arms together against the rim of the bicycle wheel. A return springs are provided for biasing the brake arms away from the bicycle wheel rim when the rider releases the brake lever. Side pull types of caliper brake devices are commonly used in road bikes.
A center pull type of caliper brake device operates similar to the side pull type, except that the brake arms are attached to a brake arm bridge such that each brake arm is pivotally coupled at a separate pivot point on the brake arm bridge. The brake arm bridge is attached directly to the frame of the bicycle. A straddle cable interconnects the two lever portions of the brake arms such that a main brake wire, which is coupled to the straddle wire, pulls the lever portions of the brake arms together.
A cantilever type of brake device is generally mounted on bicycle designs for off road use such as mountain bikes (MTB) and all terrain bikes (ATB). In particular, a cantilever type brake device is designed to provide a powerful braking force. A cantilever type of brake device is equipped with a pair of brake arms which are rotatably supported in a cantilever fashion on the front or rear fork of the bicycle frame, with the brake shoes attached to intermediate portions of the brake arms.
Typically, the lower ends of the brake arms are rotatably supported on the bicycle frame and the upper ends are linked to a brake cable or wire. The brake shoes are arranged opposite one another on either side of the bicycle wheel rim which is located between the arms. With this cantilever type of brake device, the bicycle arms rotate in the closing direction when the brake cable is pulled by the brake lever, which in turn results in the brake shoes being pressed against the rim to apply a braking force.
Cantilever types of brake devices have several advantages over side pull types of caliper brake devices. For example, with such a cantilever brake device, there is no need to vary the shape of the device with the size of the bicycle as may be the case with a side pull type caliper type brake device. Moreover, cantilever type of brake devices apply a more equal braking force than a side pull type caliper brake.
Accordingly, the present invention is especially directed to improving the performance of cantilever type brakes.
Unfortunately, cantilever type brake mechanisms suffer from their own problems. For example, if the brake shoes pivot downwardly from the horizontal plane as a result of the pivoting of the brake arms so that the brake shoes contact the side surfaces of the rim without conforming to the inclination of the side surfaces, then the pressing or braking force of the brake shoes is reduced. In other words, the brake shoes must be moved horizontally such that the slope of the brake shoes matches the slope of the rim to maintain full braking force. Consequently, it is often necessary to adjust the relative attachment positions of the rim side surfaces and the brake mechanisms with a high degree of precision. This adjustment is often difficult.
Accordingly, linkage assemblies have been utilized between the braking arms and the brake shoes to control the movement of the brake shoes from a release position to a braking position. In other words, these linkage mechanisms ensure that the brake shoes move substantially in a horizontal direction to match the slope of the bicycle rim. A brake device with a four-bar linkage assembly is disclosed in Japanese Publication No. 62-1873 that attempts to solve this problem. This four-bar link type of brake device comprises brake arms which are slidably supported on fixing pins that extend from seats, and the upper ends of which are positioned to the outside of the fixing pins, output links that are rotatably supported in the middle of the brake arms and extend to the outside, follower links that are rotatably linked to the output links and extend downwardly, and stationary links that are rotatably linked to the follower link and extend to the inside so that they are non-rotatably linked to the fixing pins.
The brake shoes are attached to the middle of the output links. With this brake device, when the brake arms are rotated upwardly by the brake cable, the follower links rotate to the inside, and the output links move horizontally or upwardly. As a result, the brake shoes hit the rim side surfaces.
With the above-mentioned structure, the frictional force of the bolt threaded into the tip of the fixing pin is utilized to link the stationary link to the fixing pin so that the stationary link does not rotate relative to the fixing pin. Consequently, when a powerful braking force is applied to the brake shoes, the stationary links are sometimes rotated against this friction by reaction forces so that the brake shoes escape from the sides of the rim, and a sufficient braking force is not obtained. Also, a sufficient braking force sometimes cannot be obtained when the links are caused to rotate by a loose bolt or by chatter. Furthermore, since the output to which the brake shoes are attached are linked in cantilever fashion to the brake arms, when a reaction force acts on the brake shoes during braking, the reaction force can cause the link portions to chatter and twist. When such chattering or twisting occurs, it allows the force that would otherwise be obtained with a four-bar linkage assembly to escape, so a powerful braking force is not obtained. Moreover, these four-bar linkage assemblies often chatter since when in the release position, since they are held in a cantilever fashion from the brake arms. Other four-bar linkage assemblies are disclosed in U.S. Pat. No. 5,636,716 to Sugimoto et al. and U.S. Pat. No. 5,655,630 to Sugimoto, both of which are assigned to Shimano Inc.
In view of the above, there exists a need for a brake device which reduces the vibrational movement of the linkage assembly. This invention addresses these needs in the art as well as other needs in the art which will become apparent to those skilled in the art from this disclosure.